Apparatus for producing sheet resinous materials

ABSTRACT

A method of making molding compounds, and particularly sheet molding compounds, wherein the reactive monomers are mixed directly with high density inorganic fillers and other ingredients of a molding compound. The monomers are converted to a resin insitu that is in or approaching the B-stage, so that the material is handleable as a solid and is moldable. Because of the amount, type, and thermal conductivity of the fillers, the resinification can be done quickly in a continuous process, by reason of the fact that the monomers are spread over a large surface area of inert fillers to provide good heat transfer, and exceedingly good process control.

This application is a division of application Ser. No. 888,261, filedMar. 20, 1978 and now U.S. Pat. No. 4,182,701, which in turn is acontinuation of application Ser. No. 751,635, filed December 17, 1976and now abandoned.

The present invention relates to a new and improved method of makingmolding compounds, and particularly sheet molding compounds. Theimproved method makes it possible to go from the mixing of monomers tothe finished molding compound in a matter of minutes as opposed to priorart processes which take hours.

BACKGROUND OF THE INVENTION

Aldehyde condensates, and particularly phenol-formaldehyde condensateswere one of the first man-made resins ever to be produced.Phenol-formaldehyde resins have found wide acceptance for making moldingcompounds because they involve readily available materials and have gooddi-electric properties. All of the phenol-formaldehyde molding compoundsthat we are aware of include organic fillers. Wood flour is mostcommonly used for a number of reasons, including the facts that: thewood flour is inexpensive and has the desirable property of absorbingwater that is liberated during the reaction, and there is a knownchemical reaction of coupling with the saw dust to provide strength. Aconsiderable amount of heat is liberated during the reaction of phenoland formaldehyde. One of the principal problems that has been involvedin the process of making phenol-formaldehyde resins has been the controlof the process to keep the temperature from running away and the resinfrom setting up in the reactor. For this reason and others, thecommercial production of phenol-formaldehyde resins has been carried outin a liquid phase in batch reactors having extensive cooling coilsand/or jackets, and in addition have been carried out in aqueoussolutions, so that the flashing of water from the mixture can beutilized to further control the reaction. Reactions in the aqueous phasecomprising approximately 40 to 50% water, require a couple of hoursbefore it reaches the A or B prepolymer stage. The prepolymer is thenblended with other materials, as for example, fillers. In the prior artprocesses wherein the reaction is carried to or approaching a B-stage,the reaction is controlled by utilizing a deficiency of formaldehyde, sothat the reaction automatically terminates without crosslinking. Suchmaterials are dried in the reactor, are poured from the reactors in amolten condition and are powdered. This novolak powder is then mixedwith a solid hydrogen acceptor, as for example, hexamethylenetetramineto form a powder mixture which will crosslink into a C or an infusiblestate. Practically all phenol-formaldehyde molding powders that we areaware of are of the novolak type. One of the reasons this is so is thatresoles tend to be so sticky and tacky that problems exist in handlingand molding mixtures of fillers and conventional resoles.

Resole aldehyde condensate resins have been used heretofore principallyas adhesives for making plywood, for binders of highly porous fibermats, and for making foams from which the water of dilution and ofreaction can be easily vented.

In this prior art background, the present invention was made.

An object of the present invention is the provision of a new andimproved process of making molding compounds wherein the startingmonomers can be transformed into a molding compound within a matter ofminutes.

Another object of the present invention is the provision of a new andimproved process of polymerizing monomers, and particularly aldehydecondensates, in a continuous controllable process as opposed to a batchprocess.

A further object of the present invention is the provision of a new andimproved process of polymerizing resins having improved controllability,by reason of better heat transfer, and physical control of thereactants, as will be seen from the following description.

A still further object of the present invention is the provision of anew and improved process for making sheet molding compound which is muchsimpler, more economical, and faster to complete.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram embodying principles of the presentinvention for making sheet molding compound;

FIG. 2 is a schematic diagram of another embodiment of the inventionwherein the fibers are spread into a layer, the monomers and fillers areapplied thereto and the monomers then reacted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to principles of the present invention, monomers for producinga polymer are dispersed throughout a relatively high percentage of asolid which the monomer will wet and particularly, inorganic inertmaterials having a heat transfer coefficient considerably greater thanthat of the resin. A sizable portion of the inert materials are of apowderous nature and provide a large surface to volume ratio, so thatthe monomers spread throughout and coat the surface of the inertmaterials in a relatively thin layer. Thin solutions ofphenol-formaldehyde condensates are normally very sticky, but these samecondensates when dispersed throughout a volume of inert materials, andparticularly inorganic fillers, provide a plastic mix, the surface ofwhich is relatively nontacky. By dispersing at least one of the monomersthroughout the inert fillers as a solid, contact between the monomerscan be controlled by a kneading action. By kneading the materials duringtheir reaction in a manner which moves the center of the mass to theoutside surface, and moves the outside materials to the center of themass, heat transfer to external surfaces can be made to take place at arelatively rapid rate. A reaction which would normally require severalhours in a reaction kettle using the best presently available equipmentcan be carried out in approximately 10 minutes utilizing the abovementioned principles.

The process lends itself to a continuous operation which can becontrolled and terminated by cooling the reaction to stop it at eitheran A-stage or a B-stage. The method has particular advantages when usedto polymerize an aldehyde and a hydrogen donor as for example a phenol,urea, melamine, dicyandiamide, and the other materials with whichaldehydes can be reacted and condensed. The present invention, however,can be used for the polymerization of other polymers, for example,polyesters, polyurethanes, polyamides, etc. In some polymer systems,wherein one type of chemical reaction is utilized to produce the linearprepolymer and another type is utilized to produce the crosslinkedpolymer, it may be desirable to add the crosslinking monomer to the mixafter the first stage reaction has proceeded to a desired level.

As previously indicated, the principles of the present invention haveparticular advantages in the production of sheet molding compounds. Thereaction materials after approximately 10 minutes of mixing can becaused to be in the form of a paste that can be fed to a conventionalsheet molding compound machine. In this machine a thin layer is appliedto a separation sheet, a layer of chopped inorganic fibers is placed ontop of the paste and another thin layer of plastic mix is brought downon top of the layer of glass fibers. The resulting sandwich is kneadedtogether in a well-known manner to produce what is known as sheetmolding compound. Because the inorganic fillers are wetted out in themonomer stage, the present invention makes it possible to carry out theinitial polymerization to a much higher molecular weight, if desired;the coating of the filler particles by the resin is no longer a problemduring mixing; and maturation, therefore, can be held to a relativelyshort period, or can be done away with entirely. In the case of aldehydecondensates, B-staging can be done during the initial reaction time, orcan be completed by a short heating period after the sheet moldingcompound is made. The present invention makes it possible to carry outthe initial polymerization to a solid B-stage wherein the materials canbe caused to crumble and subdivide, by reason of the fact that they aredispersed throughout and continually kept in motion with a large volumeof inorganic filler. This material can be granular in nature so that alayer of the granular mix can be placed on a moving surface, a layer offibers put on top thereof, and another layer of the granular materialson top of the fibers in what may now be termed a dry method of making asheet molding compound. After the layers are put together in a drycondition, they may be heated to fuse the resin. Upon cooling, a rigidsheet is produced which can be fed to a press as a solid sheet, andconverted to the C, or infusible state.

The present invention makes it possible to produce a sheet moldingcompound utilizing aldehyde condensate binder, as for example a phenolformaldehyde binder in approximately 10 minutes. By appropriatelychilling mixes of the present invention utilizing A-staged condensates,it is possible to avoid tack problems, and so not use the plasticseparation sheets used by the prior art. This is an advantage byallowing a maximum amount of water to be removed from the moldingcompound prior to the time that it is put in a press.

In general, the fillers may comprise from 50% to approximately 90% byweight of the resin-filler paste solids. An inorganic fiberreinforcement may be used up to approximately 30% of molding compoundcomprising the fibers, resin and fillers. Any granular and/or powderousinorganic filler can be used. The term phenol will be understood tocover any compound having an OH group affixed to an aromatic ring thathas at least 3 lable hydrogens affixed thereto.

EXAMPLE 1

Because the present invention has so many advantages when used inconjunction with aldehyde condensate binders, details of the processwill now be explained in conjunction with the production of aphenolformaldehyde binder.

A sheet molding compound was made from the following materials in partsby weight:

    ______________________________________                                        Materials                Parts by Weight                                      ______________________________________                                        Calcium carbonate (minus 100 mesh)                                                                     105.0                                                Phenol (ground to powder)                                                                              38.2                                                 Paraformaldehyde         18.2                                                 Calcium hydroxide        3.6                                                  Zinc stearate (mold release agent)                                                                     1.5                                                  Coupling agent (gamma aminopropyltrimethoxy-                                                           0.9                                                  silane)                                                                       Water                    7.0                                                  ______________________________________                                    

The sheet molding compound is made using the procedure shown in FIG. 1.The calcium carbonate, powdered phenol, calcium hydroxide, and zincstearate are added to the blender 10 and thoroughly mixed. Thereafter,the solid blend is conveyed to the storage hopper 12 from which it isfed onto a constant delivery belt 14 whose speed can be adjusted toprovide a desired rate of solid materials discharge. The solid materialis delivered to a progressing cavity pump, as for example a Moyno pump,that is steam jacketed for approximately one third to one half of itslength to supply heat to the mixing material and initiate the reactionof the phenol and the aldehyde. The paraformaldehyde is continuouslyadded to the constant delivery belt 14 immediately before its deliveryto the progressive cavity pump and a small spray of water is added tothe pump inlet in order to hasten contact between the phenol,paraformaldehyde and calcium hydroxide catalyst, all of which aresolvated by the water. Once the reaction is initiated at about 85° C.,an exotherm is produced, and the reaction continues for approximately 10minutes. The rotor of the progressive cavity pump 16 is rotated at aslow controlled rate of speed to provide a slow mixing of theparaformaldehyde, phenol and catalyst throughout the reaction tosimultaneously move the materials that are adjacent the rotor outwardlyto the heat transfer surface, and vice versa. The last half of theprogressive cavity pump 16 is jacketed as at 20 for cooling water.Cooling is used to stop the reaction at a stage where the exitingmaterial has the desired paste viscosity for subsequent flow aroundchopped glass fibers as occurs in producing sheet molding compounds.This viscosity will generally be below 50,000 centipoise and preferablyapproximately 20,000 centipoise, depending upon the amount of water thatwas added with the monomers, and the amount of vaporization which takesplace prior to making the sheet molding compound. In some instances,when very little water, if any, is utilized, polymerization of thephenolformaldehyde prepolymer will be stopped at slightly more than anA-stage. When appreciable amounts of water are present, thephenolformaldehyde prepolymer will be stopped at slightly less than aB-stage. In the present instance, the material is slightly more thanA-staged, and is spread out on a moving belt 22 by a doctor blade 24into a layer approximately 1/8-inch thick. Thereafter, chopped glassfiber strand having a length of approximately 1-inch is fed onto thelayer of paste by direct fall from a strand chopper 26. Thereafter, theendless belt 22 moves material underneath another continous flexiblebelt 28, and compaction rollers 30 above and below the two endless beltssqueeze the fibers into the paste. Heaters 32 are positioned above thebottom run of the endless belt 28, and below the top run of the endlessbelt 22 to raise the temperature of the material to again initiate areaction, which changes the A-staged prepolymer into substantially apartially B-staged material. Thereafter, the endless belt moves themixture between chillers 34, one of which is positioned above the bottomrun of the endless belt 28 and the other one of which is positionedbeneath the top run of the endless belt 22. The chillers bring thetemperature of the material down, to arrest the reaction, and increasethe viscosity of the sheet molding compound to such a degree that theendless belt 28 and the endless belt 22 can be separated from the sheetmolding compound without sticking.

Thereafter, the sheet molding compound passes to an open meshed endlessbelt 36, the top run of which passes between a pair of heaters 38 towhich a partial vacuum is communicated to flash off unwanted water andbring the sheet molding compound to a substantially dry handleablestate. Not all the water need be removed, however, The sheet moldingcompound is then moved by the open meshed belt 36 to between a pair ofchillers 40 which solidify the now substantially B-stagedphenolformaldehyde binder and in turn cause the sheet molding compoundto become boardlike and self-supporting.

The sheet molding compound so made needs further maturation. Sheetmolding compound containing 15% chopped glass strand when molded at2,000 psi for 5 minutes between metal dies heated to 350° F. provides afluxural strength of 15,200 psi, and a flexual modulus of 1,920,000.

EXAMPLE 2

The process of Example 1 is repeated excepting that a 52% formalinsolution is substituted for the paraformaldehyde and water. In thiscase, the formalin is added by spraying into the entrance of theprogressive cavity pump. The temperature of the reaction is slightlyhigher than in Example 1 and the prepolymer is advanced to a slightlyhigher degree of cure, so that approximately the same viscosity of thepaste is maintained even though more water is present. Also in thisinstance, the heaters 38 are controlled to remove the additional amountof water that is present by reason of the replacement of theparaformaldehyde by the formalin. Parts molded from the sheet moldingcompound so produced have substantially the same properties as do thoseof Example 1.

EXAMPLE 3

The materials given in Example 1 exclusive of the water is made into asheet molding compound using the procedure of FIG. 2. According to themethod shown in FIG. 2, the calcium carbonate, powder phenol, calciumhydroxide, and zinc stearate are added to the dry material mixer and areblended together. The blend of dired materials is conveyed by theconstant delivery belt 14a to the endless conveyor 22a. Theparaformaldehyde monomer is added continuously to the constant deliverybelt 14a just before the materials fall onto the sheet molding compoundforming conveyor 22a. In this embodiment, the chopped glass fibers fromthe chopper 26a are placed onto the endless belt 22a and the driedmaterials are applied over the top of the layer of chopped fibers whichsupports the dry materials to some degree. The fibers and powders arethen moved by the endless belt 22a into a heater 32a which melts thephenol and brings it into contact with the catalyst and paraformaldehydeto start the condensation reaction. Water is generated a movement ofgases through the fibers sweeps water vapor from the materials. Thespeed of the conveyor and amount of heat added in the heater 32a iscontrolled so that the reaction continues for approximately 10 minutes,after which time the prepolymer will have advanced to almost a B-stage.Thereafter the belt 22a moves the layers into a cooler 34a which bringsthe temperature down to stop the reaction and increase the viscosity ofthe prepolymer to a non-tacky state. The filler and binder are thencompressed into the layer of fibers by the compression rolls 42 toproduce the sheet molding compound. Parts molded from the sheet moldingcompound using the procedure as given in Example 1 has substantially thesame physical properties as does the material of Example 1.

EXAMPLE 4

A sheet molding compound is made from the following materials utilizingthe procedure of Example 1:

    ______________________________________                                        Materials       Parts By Weight                                               ______________________________________                                        Water           16.68                                                         Portland Cement 62.83                                                         Phenol          30.49                                                         Paraformaldehyde                                                                              24                                                            ______________________________________                                    

The sheet molding compound is made by mixing the portland cement with7.89 parts of water which is then left standing for 5 days to hydrate.The material is then ground into a fine powder, is charged to theblender 10 along the powdered phenol. This mixture is then charged tothe progressive cavity pump along with the paraformaldehyde powder, and8.79 parts of water is sprayed into the mixture as it is added to theprogressive cavity pump. No mold release agent is utilized, the parts ofthe mold are coated with a mold release agent. The parts so producedwhen containing 15% by weight of 1-inch long chopped glass fiber strandhave substantially the same strength as do the parts produced accordingto Example 1.

EXAMPLE 5

A sheet molding compound is made from the following materials using theprocedure of EXAMPLE 1:

    ______________________________________                                        Materials          Parts By Weight                                            ______________________________________                                        Calcium Carbonate Powder                                                                         100                                                        Ca(OH).sub.2       24                                                         Paraformaldehyde   80                                                         Urea               100                                                        ______________________________________                                    

The sheet molding compound is made using the procedure of Example 1using approximately 30 percent by weight of 1/2-inch chopped glass fiberstrand. This material produces acceptable molded parts having excellentflame resistance with somewhat less strength than does the partsproduced by Example 1.

EXAMPLE 6

A sheet molding compound is made from the following materials using theprocedure as given in Example 1:

    ______________________________________                                        Materials       Parts By Weight                                               ______________________________________                                        Calcium Carbonate                                                                             100                                                           Ca(OH).sub.2    24                                                            Paraformaldehyde                                                                              48                                                            Melamine        100                                                           ______________________________________                                    

The sheet molding compound made using these materials and moldedaccording to the procedure of Example 1 has low smoke production andgood flame resistance, but somewhat less strength than does the moldedparts of Example 1.

EXAMPLE 7

A molding compound is made using the procedure of Example 1 from thefollowing materials:

    ______________________________________                                        Materials       Parts By Weight                                               ______________________________________                                        Furfural        101.8                                                         Phenol          100                                                           Calcium Carbonate                                                                             600                                                           Ca(OH).sub.2    8                                                             Zinc Stearate   8                                                             ______________________________________                                    

Molded parts made from this sheet molding compound using the procedureof Example 1 has strength generally comparable to those of Example 6.

EXAMPLE 8

A sheet molding compound is made from the following materials using theprocedure of Example 1:

    ______________________________________                                        Materials       Parts By Weight                                               ______________________________________                                        Calcium Carbonate                                                                             600                                                           Phthalic Anhydride                                                                            148                                                           Glycerol        62                                                            Zinc Stearate   8                                                             ______________________________________                                    

The phthalic anhydride, calcium carbonate, and zinc stearate are mixeddry in the blender 10, and the glycerol is added to the progressivecavity pump with a slight amount of water and catalyst to initiate areaction when heated. The throughput of the pump is controlled so thatthe material is cooled to stop the reaction before the material reachesa B-stage and while the viscosity is approximately 5,000 centipoise. Thetemperature in heater 32 is controlled to bring the material to nearly aB-stage and excess water is removed by the heater 38 to produce aflexible sheet molding compound. The materials when molded using 15% byweight of 1-inch chopped glass fibers has properties comparable withconventional sheet molding compound.

It will be seen that the process and apparatus of the present inventionhas particular advantages for making molding compounds, and particularlysheet molding compounds, from materials, which liberate troublesomewater or gases during polymerization. In the most preferred method,monomers are used as the starting reactants and the reaction is carriedout in situ with fillers to produce an A-stage or linear prepolymer thatis flowable and which makes a tacky paste with the filler. According tofurther principles of the invention, the paste is then mixed withfibrous reinforcement while the prepolymer is in the liquid A-stage,which for aldehyde condensates is water soluble. Inorganic fibers arewetted by water and evaporation is preferably done in the presence ofwater and water soluble prepolymers. Unfortunately, these A-stagedmaterials become tacky and sticky in all but dilute solutions.

In the next stage of molding compound preparation, the prepolymer isadvanced in cure to a stage wherein the tack is reduced sufficientlythat the compound can be removed from plastic surfaces. This requiresthat the prepolymer approach a B-stage wherein its molecules areessentially linear, but are chain extended to a degree that they arefusible, soluble in organic solvents, have greatly reduced solubility inwater, and will separate from plastic surfaces. These properties can beachieved even though the prepolymer is intermediate the A and B stages.

In the last stage of preparation, the prepolymer is advanced tosubstantially a full B-stage wherein it is essentially crosslinked andnon water soluble. This allows as much water as possible to be removedfrom the finished molding compound. At this stage, the top belt isremoved and the bottom conveyor means is preferably porous to permitthis water to be removed quickly. The finished molding compound,therefore, has a minimum of water and/or gases which must be removedwhen the molding compound is actually molded. Molding, of course, isdone between heated compression surfaces; and liberation of water and/orgases at this stage. can be very troublesome, and may damage the partsproduced.

While the invention has been described in considerable detail, we do notwish to be limited to the particular embodiments shown and described,and it is our intention to cover hereby all novel adaptations,modifications, and arrangements thereof which come within the practiceof those skilled in the art to which the invention relates.

We claim:
 1. Apparatus for preparing sheet molding compound comprising:conveyor means with an impervious upper surface thereon for advancingtacky material past curing stations, and endless belt having animpervious surface and a bottom run spaced above said conveyor means,means for depositing a tacky prepolymer containing material and afibrous reinforcement therefor on said conveyor means ahead of saidendless belt, means biasing said endless belt toward said conveyor meansto embed the reinforcement into the prepolymer containing material,first heating means for heating the material between the conveyor meansand endless belt to initiate a reaction of the prepolymer, first coolingmeans for cooling the material between the conveyor means and theendless belt to control advance of the initiated reaction of theprepolymer prior to the end of the bottom run of the endless belt,second heating means for heating the materials on said conveyor meansfollowing exiting from said endless belt to again initiate furtherreaction of the prepolymer containing material to a still crosslinkable,sheet handleable condition, and second cooling means for cooling thematerial discharged from said heating means to arrest polymerization ofsaid prepolymer containing material in its crosslinkable condition. 2.The apparatus of claim 1 wherein said conveyor means comprises animpervious endless conveyor beneath said endless belt and an open meshbelt for carrying the material through said second heating and coolingmeans.
 3. Apparatus for producing sheet molding compound, comprising:impervious and pervious endless conveyors arranged end to end with saidimpervious conveyor being arranged to discharge onto said perviousconveyor, an endless belt having an impervious surface with its bottomrun spaced above said impervious endless conveyor by a predetermineddistance, feed means for depositing a tacky prepolymer containingmaterial in a layer on said impervious endless conveyor ahead of saidendless belt, heating means for heating the layer of prepolymercontaining material on said impervious conveyor sufficiently to initiatea reaction of the prepolymer, cooling means following said heating meansfor cooling said layer sufficiently to cause it to separate from saidimpervious conveyor before discharging onto said pervious conveyor,heating means for advancing the cure of the layer on said perviousconveyor to a nontacky state, and cooling means for cooling the layer onsaid pervious conveyor sufficiently to form a handleable sheet.
 4. Theapparatus of claim 3 including means for subjecting the heated portionof said pervious conveyor to a partial vacuum to remove water from thelayer of material on said conveyor.
 5. The apparatus of claim 3 whereinsaid feed means comprises: a progressive cavity pump the inlet end ofwhich receives reactants and the discharge end of which discharges tosaid impervious conveyor, said pump having a heating jacket adjacent theinlet end for initiating reaction of materials therein and a coolingjacket preceding the discharge end for arresting reaction of materialstherein before discharge.
 6. Apparatus for producing sheet moldingcompound, comprising: a progressive cavity pump having an inlet end anda discharge end with a heating jacket adjacent its inlet end and acooling jacket adjacent its discharge end, solid material feed controlmeans for fillers and polymer producing reactants discharging into saidpump inlet, an impervious endless conveyor fed by the discharge of saidprogressive cavity pump, a pervious endless conveyor fed by saidimpervious endless conveyor, means distributing materials fed from saidprogressive cavity pump in a layer on said impervious endless conveyor,an endless belt having an impervious surface with its bottom run spacedabove said impervious endless conveyor to confine said layer betweensaid impervious surfaces, heating means for initiating a reaction of thereactants in the layer between said impervious surfaces, cooling meansfollowing said heating means for cooling said layer sufficiently tocause it to separate from said impervious surfaces, heating means forinitiating a further reaction of materials on said pervious conveyor toadvance the cure in said layer to a nontacky state, and cooling meansfor cooling the layer on said pervious conveyor to a handleable state.7. The apparatus of claim 6 including means for subjecting the layer onsaid pervious conveyor to a partial vacuum.